Abstract

Although the molecular mechanisms underlying the pathogenesis of Alzheimer's disease
and other related neurodegenerative diseases remain unclear, accumulation of misfolded
proteins, neuroinflammation, mitochondrial dysfunction and perturbed calcium homeostasis
have been identified as key events leading to neuronal loss during neurodegeneration.
Evidence for 'druggable' targets for each of these key mechanisms was presented by
the Alzheimer's Drug Discovery Foundation-funded investigators at the 12th International
Conference on Alzheimer's Drug Discovery, Jersey City, NJ, 26-27 September 2011 http://www.worldeventsforum.com/addf/addrugdiscoverywebcite.

Meeting report

A wide variety of novel therapeutic strategies were presented at the 12th International
Conference on Alzheimer's Drug discovery hosted by the Alzheimer's Drug Discovery
Foundation (ADDF). This report highlights novel strategies funded by the ADDF that
are progressing through the drug development pipeline (Figure 1).

Neuroprotective strategies

Therapies that are neuroprotective or neurotrophic and can protect against neuronal
loss are attractive targets in preventing or slowing the progression of Alzheimer's
disease (AD). Carmela Abraham (Boston University School of Medicine, USA) discussed
the development of modulators of Klotho expression, a protein that has been shown
to decrease with age and regulate maturation of myelinating oligodendrocytes. Three
hit compounds were identified from a high-throughput screen (HTS) of 150,000 compounds
that inhibit methylation at CpG islands and thereby increase Klotho expression. Hits
have been validated in several cell lines and are now undergoing a medicinal chemistry
strategy to ensure a desirable pharmacological profile. A second neuroprotective strategy
was highlighted by Eugenia Trushina (Mayo Clinic College of Medicine, USA). Trushina
and team identified and characterized an orally available and blood brain barrier
(BBB) permeable tricyclic pyrone, CP-2, which eliminates 80% of amyloid deposits (fibrillar
and oligomers) in the 5× familial AD (FAD) transgenic model. Probing the mechanism
of action revealed metabolomic changes and altered mitochondrial trafficking and function
prior to the onset of memory and neurological phenotypes, all of which were reversible
with CP-2 treatment.

Other novel neuroprotective strategies targeted neuroinflammation through the orally
available tetramethyl-pyrazine (TMP), derived from a Chinese medical herb (Ziqun Tan,
University of California, USA). Martin Watterson (Northwestern University, USA) presented
the development program for MW151, a small molecule modulator of p38α mitogen-activated
protein kinase (MAPK) activity in neuronal and glial cells with 'druggability' at
the forefront of development. Watterson and colleagues undertook a strategic medicinal
chemistry program to address the major barriers to AD therapeutics: central nervous
system penetrance and undesired pharmacology. This program resulted in the development
of MW151, a highly selective, BBB penetrable compound that effectively attenuated
pro-inflammatory cytokine production and reversed behavioral deficits following oral
administration in an amyloid-β-induced brain injury mouse model.

Robert Mahley (University of California, USA) presented an update on PY101, a small
molecule that restores apolipoprotein E4 (ApoE4) to an ApoE3-like structure. Ten-day
oral administration of PY101 in the neuron-specific enolase ApoE4 (NSE-ApoE4) mouse
model resulted in decreased production of toxic ApoE fragments and increased mitochondrial
cyclooxygenase-1 levels in the hippocampus. Identification of this toxic gain of function
for ApoE4 opens up additional targets in this pathway, including protease inhibitors
to prevent neuron-specific proteolysis of ApoE4 and mitochondrial protectors to prevent
ApoE4 fragment interaction with mitochondria. Finally, the most advanced of these
neuroprotective strategies, in phase II/III for the orphan neurodegenerative disease
progressive supranuclear palsy (PSP), was presented by Illana Gozes (Allon Therapeutics,
USA). Allon Therapeutics' drug (davunetide), a short eight amino acid fragment of
activity dependent neurotrophic factor (ADNF), met limited efficacy end-points in
a phase II AD trial, but is now being tested in an improved formulation for PSP.

Calcium homeostasis and plasticity

Histone deacetylase (HDAC)2 has been previously implicated in memory formation and
synaptic plasticity; however, the development of HDAC2-specific inhibitors has been
challenging. To reduce the toxicity associated with this class of compounds, Pavel
Petukhov (University of Illinois, USA) screened compounds using Binding Ensemble Profiling
with Photoaffinity Labeling to specifically identify compounds that bind in an orientation
that prevents chelation of the zinc group. This screen identified a lead compound
with an improved pharmaco-kinetic and toxicity profile.

Altered calcium homeostasis, specifically increased endoplasmic reticulum calcium
release, has been linked to a number of sporadic AD risk factors and is thought to
underlie altered synaptic transmission and plasticity. Grace Stutzmann (Rosalind Franklin
University School of Medicine, USA) and colleagues were the first to observe that
the endoplasmic reticulum-resident ryanodine receptor (RyR) differentially regulates
synaptic transmission and plasticity in non-transgenic and AD transgenic mice. Chronic
treatment of 3× FAD transgenic mice with the RyR antagonist dantrolene (injection)
normalized calcium signaling by preventing increased endoplasmic reticulum RyR-mediated
calcium release, validating RyR as a potential target for further screening.

Protein folding and degradation

Heat shock proteins (HSPs) promote the correct folding and refolding of misfolded
proteins, including tau, amyloid-β, and α-synuclein, and are therefore attractive
targets for a number of neurodegenerative diseases. Several approaches to target HSP70
and HSP90 were presented. Allen Reitz (ALS Biopharma, USA) identified hit compounds
that lowered tau levels by inducing HSP70 expression in human glioblastoma cell lines.
Understanding the mechanism of action of a target is vitally important during drug
design. This point was highlighted by Chad Dickey (University of South Florida, USA),
who discovered that inhibition of HSP70 ATPase activity could also be effective at
stabilizing disorganized tau. Inhibitors from a HTS based on rhodacyanine dyes have
now been validated for their ability to decrease tau accumulation and rescue long-term
potentiation in hippocampal slice cultures from Tg4510 tau mice. A second member of
the heat shock family, HSP90, was the focus of Gabriela Chiosis's (Memorial Sloan
Kettering Cancer Center, USA) drug discovery program. Chiosis identified two populations
of HSP90 in pathogenic or stressed tissue (tumors and dystrophic neurons); a good
housekeeping HSP90 complex and an HSP90 complex that selectively binds to pathogenic
protein. Hsp90 inhibitors developed by this team specifically bind the pathogenic
HSP90 complex and reduce total tau and phospho-tau following acute treatment in the
3× FAD transgenic mouse model. Chronic studies will be required to assess behavioral
outcomes.

Dysfunctional protein degradation pathways contribute to neurodegeneration. Karen
Duff (Columbia University, USA) provided target validation for autophagy and proteasome
targets demonstrating that mice with progressive tauopathy show a decline in proteasome
function concomitant with an induction of autophagy and accumulation of fibrillar
tau aggregates. In vivo induction of autophagy following acute oral administration of trehalose, a non-reducing
dissacharide, effectively decreased tau pathology in the P301L tau mouse model. Duffnoted
that the decreased proteosomal function seen during the onset of pathology could be
reversed pharmacologically, highlighting both autophagy and proteasome activation
as two potential drug targets in stimulating clearance of protein aggregates that
present in numerous neurodegenerative diseases.

Lysosomal function plays a critical role in protein clearance. Lysosomal storage diseases,
such as Gaucher disease, Fabry disease and Sandhoff disease, show evidence of accumulated
intraneuronal amyloid-β in addition to decreased lysosome enzyme function. Brandon
Wustman (Amicus Therapeutics, USA) and team have developed a set of novel pharmacological
chaperones that enhance the activity of critical lysosomal enzymes, are orally available,
cross the BBB, and are currently in phase III for Fabry disease. Now, Wustman and
team are testing a novel, potent pharmacological chaperone for its effects in clearing
intraneuronal amyloid-β in an animal model of cerebral amyloid angiopathy, an orphan
indication with relevance to AD.

Novel biomarkers

The development of novel biomarkers to accurately diagnose AD prior to clinical manifestation
and to predict conversion from mild cognitive impairment to AD is essential for the
development of new therapeutics and understanding mechanisms of disease progression.
Currently, the only definitive diagnostic tool for AD is at autopsy. The most developmentally
advanced imaging biomarker, AV-45 (florbetapir), is currently up for approval by the
US Food and Drug Administration (FDA). Daniel Skovronsky (Avid Radiopharmaceuticals,
Inc., USA), funded by the Alzheimer's Drug Discovery Foundation (ADDF) for the initial
stages of development of florbetapir-positron emission tomography (PET), provided
the opening plenary address. Florbetapir 18F is a PET imaging agent with high specificity for amyoid-β binding. Skovronksy presented
data from longitudinal analysis of normal older people with positive florbetapir-PET
scans and identified a correlation between scan positivity and cognitive decline in
normal older people, providing further evidence that amyloid-β load correlates with
cognitive function.

Diagnostic tests that correctly diagnose different causes of dementia are clinically
challenging and remain a critical unmet need. Biomarkers that efficiently distinguish
between frontotemporal lobar degeneration (FTLD) with TDP43 (TAR DNA-binding protein
43) or tau pathology are necessary for the development of disease-modifying treatments
and to identify patients for inclusion/exclusion from clinical trials. William Hu
(Emory University School of Medicine, USA) provided an update on the program to identify
relevant biomarker(s) using a targeted proteomics approach. Hu and colleagues identified
a panel of analytes from cerebrospinal fluid samples that potentially distinguish
between FTLD with TDP43 pathology and FTLD with tau pathology. The team is currently
recruiting patients for a multi-center study to validate this panel. Je Kuret (Ohio
State University, USA) presented data on a HTS to identify selective radiolabeled
compounds with high selectivity for tau by utilizing amino acid side chains of cross-β-sheet
aggregates to increase binding selectivity. The team has identified potent lead candidates
currently under optimization.

Allen Roses (Duke University, USA) highlighted the utility of biomarkers to enrich
patient populations in clinical trials. Roses and team have identified a region on
chromosome 19 next to APOE that encodes the mitochondrial protein TOMM40 (translocase of outer mitochondrial
membrane 40 homolog) and can help explain the age-of-onset variability within the
APOE genotype. Through an algorithm-based approach, Roses and team are testing the prognostic
value of the TOMM40 genotype, APOE variants and age for patient inclusion in a trial of pioglitazone in normal subjects.
To close the program, José Luchsinger (Columbia University, USA) presented the use
of [18]F-labeled 2-deoxy-2-fluoro-D-glucose (FDG) PET with magnetic resonance imaging as
a secondary endpoint for an ongoing phase II clinical trial for the anti-diabetic
metformin in patients with mild cognitive impairment.

The ADDF drug discovery portfolio encompasses a wide spectrum of novel targets in
the generation of therapeutics for the treatment of AD and related dementias. The
work presented highlights the innovative approaches required during preclinical and
clinical development. The ADDF will continue to support novel targets in order to
achieve our mission to conquer AD through drug discovery. Please join us for our 13th
annual International Conference on Alzheimer's Drug Discovery in the Fall of 2012
in Jersey City, NJ, USA.

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

This conference would not have been possible without the generous support of our sponsors:
Pfizer Inc., Eli Lilly and Company, Elan Pharmaceuticals, Merck Research Laboratories,
Allon Therapeutics, NeuroPhage Pharmaceuticals, JSW Life Sciences, Abbott Laboratories
and Genentech.